If variation in a heritable trait is associated with variation in reproductive success…
those traits accumulate in population
Brainstorm: What traits might be associated with mating decisions between males and females in the animal kingdom?
Natural selection is way broader than you thought!
Darwin proposed models of sexual selection
Sexual selection is one kind of natural selection
Selection can occur as an association between phenotype and mating success
secondary traits in mating
Sexual Dimorphism = males and females look different
Introduces choosiness into evolution and reproduction
‘mate choice’
Often: male ‘showiness’ in nature
benefits versus risks…
Is this why males look and behave differently?
Intrasexual selection is the battleground for mating
‘Choosiness’ leads to competition
Occurs among males in many species
Direct combat
Subtle combat
Display (rituals and colors)
Drives the evolution of secondary sexual characteristics
between males
Direct Combat: Stag beetles (Goyens et al. 2016)
Subtle combat
Often post-copulatory sperm competition
selection of diverse and elaborate male genitalia
Common in insects
Piskin and Koskin 2010
Common in birds
“Many bizarre traits, including male genitalia that explode during copulation, male genitalia that “sing” during copulation, potent seminal products that invade the female’s body cavity and her nervous system to influence her behavior…. Eberhard 2009"
Subtle combat
Male displays and rituals (birds of paradise)
Male displays and rituals (widowbird)
Male displays and rituals (bowerbirds)
Why is there sexual dimorphism?
Why be choosy?
what are the real rewards for the female?
How common is choosiness??
Sexual selection results in the evolution of sexually dimorphic traits
preferential mating
direct fitness benefit
indirect fitness benefit
Heterosexual conversation….for now
Female guppies prefer males with orange spots….Why?
Female blackbirds prefer males with orange beaks.. Why?
Brainstorm: Why do animals prefer symmetric partners?
